Electrical circuits



M. D. RUBIN ELECTRICAL CIRCUITS April 3, 1951 3 Sheets-Sheet 1 Filed May 25, 1948 OUTPUT VOLTAGE April 3, 1951 M. D. 4RLJBIN ELECTRICAL CIRCUITS 3 Sheets-Sheet 2 S om? Y /M/ENTOR M/LToA/ D. Rus/N -y nro EY Filed May 25, 1948` April 3, 1951 M. D. RUBIN ELECTRICAL CIRCUITS 3 Sheets-Sheet 3 Filed May 25, 1948 T w T Mwnwy rw 0. w 7 N A 0 T vl ma y Patented Apr. 3, 1951 YUNITED VSTATES `iPlA'TEI'F'l yOFFICE Milton D. Rubin, Dorchester, Mass., assignorto `Raytheon Manufacturing Company, Newton,

Mass., a corporation of Delaware Application May 25, 1948,V Serial No. 29,004

i suchv that, if the systemis. in a state in which no servo information. is being generated, the .system will sweep through all possible states in succession until it doesV come into. a regionof operation .in which servo information is generated, after which .it Awill oscillate in asmallneighborhood about .the

desired state. y

An additional object is to devise a servo system in which the error detector of the system need not have sense; that is, its output neednot have opposite polarities above andbelow. its rcenter value.

'Yet another object is to devise. a'. novel error -Qdetectorfor an automaticfrequency control servo system.

Still another object is to devise a novel .clamp- '..ing circuit arrangement Whichiis useful in con- 1 nectionwith a blocking oscillator. Y

Another objectisto vprovide a sweep circuit ..2.1 utilizing a condenser which is chargedin a novel .1. manner to .provide aV .desired voltagek variation thereon. y

.A further objectis .to devise a novel system for causing the voltage on. a condenser-'to oscillate 'l back and forth through a small range-about a L desired value.

The foregoing and other objects ofthe inven- -tion will be best understood from the following description of an exemplification thereof, reference being had to the accompanying drawings, wherein: Figs. l. and 2 are curves useful .in explainingthe operation of the invention;

Fig. 3 is a combined schematic and "blockdiagram of. a servo system embodying the invention;

Fig. 4 is a circuit diagram of an embodiment of this invention; and

Figs. 5 9 represent waveforms occurring under various conditions and at various points inthe circuit of Fig. 4. q

Y' In certain systems which usea local oscillator v'for mixing or for other purposes,'itis desired that `.the output' frequency of lthe said oscillat'orf not 'vary'morethan a-small-amount Von eitherside of 16 Claims. (Cl. 2450436) a predetermined-frequency to which the oscillator has been. adjusted. If the local oscillatorv is a f reeXKlyistron,-as disclosed illustratively herein, Alundesired@variations or discrepanciesin the outputl frequency may resultV from changes inlthe internal dimensions of the Klystrons resonant cavity, from changes in the resonator potential,

v4'cnrffrom othercauses. The present invention provides Van automatic frequencycontrol .system for such a local. oscillator. .f For the. purposes of the present invention,4in

Mwliichlthe-.local `oscillator may have a frequency on the order of 9,000megacycles, `for example,.the

frequency used dictatesthe choice of a'resonant f, cavity. asa sufficiently. rugged, simple andreliable reference standard of frequency. Y A. portion ofthe output ,signal of the oscillator,.-the

frequency of-'whichis to be-controlled, is-passed ris-:of the-transmission type,. the output as a function. offfrequencyis` asl-represented by curve A through the.reference cavity, and the rectified output of the cavity `is examined. If .the cavity win. Fig.; 1,.Y a. symmetrical `resonance curve. centered'attheresonant frequency of the cavity. In

such a casa-the :magnitude of therectified output of the cavity indicatesV the degree of error from A the cavityresonant frequency but not .the direction` therefrom. However, if the frequency of the @signal feeding rinto the lcavity .is modulated rof the output isthe-.same as thatv of the-modulation signal ofthe input if the carrieror restffreslightly, the sign-of the rectified modulation sig-nal Vquency 4is inthe'region ofpositive slope ofthe yresonance curve A,- and vice versa if inthenegative slope.y region of. said curve, thusv indicating whether the signal is above .or below-thecavity resonant frequency. vBy this means, both direction and degree of error are indicated-bythe `output of the cavity, and correction can be applied tothe oscillator. accordingly.

- According Vto this invention, pulse frequency modulation isA used instead of sinusoidalor other type of .continuousfrequency modulation, in order to. eliminate' the V`phase--dtermining on. phasecomparison devices necessary with such-continuf Aous .frequency modulation. VIn Fig. 1, consider pulse frequency modulation input signal. B

which .isvapplied when the carrier or.. rest-ffrequency is below the resonant frequency rof curve A or in the region of postiveslope thereof. `4Such an input signal `will produce a rectified. output modulationsignal of the character showntfat C,

. the amplitude tof. thisisignalfbeing determined; by

projecting the upperand:lowerfrequencylimits output `limits 'for outputipulseC,.andthelength of signal.. B torfcurve. A to obtain corresponding time)y ofpulse signaLC 4beingequalto"that thereto.

of signal B. Under these conditions (when the carrier or rest frequency is below the resonant frequency), the output pulse C is of the same sign as the input pulse B.

Now consider a pulse frequency modulation input signalD which is applied lwhen the carrier or rest frequency is above the resonant frequency of curve A or in the region of negative slope thereof. Such an input signal will produce a rectified output modulation signal of the character shown at E, the amplitude of this signal being determined by projecting the upper and lower frequency limits of signal D to curve A to obtain corresponding output limits for output pulse E, and the length (in time) of pulse signal E being equal to that of signal D. Under these conditions (when the carrier or rest frequency is above the resonant frequency), the output pulse E is of the opposite sign to input pulse D.

' As illustrated by Fig. 2, there is some ambiguity when the rest or carrier frequency is near the resonant frequency. Consider a pulse frequency modulation input signal F which is applied at such a point with reference to the carrier or rest frequency as to span the resonant frequency of curve A. Such an input signal will produce a rectified output modulation signal of the character shown at G, the amplitude and time width of this signal being determined as described hereinabove. Pulse output signal G contains both minus and plus portions, so that in this situation there is some ambiguity as to the direction of error. However, the narrow positive portions of output signal G can be substantially eliminated in succeeding circuits if the rise and fall times of input pulse F are considerably less than the duration of the flat top thereof; in this way, the ambiguity may be removed. It should be noted that even though the base line of' input signal F is below the cavity resonant* frequency, the output signal G is of opposite sign to the input signal F, or is reversed with respect This means that the target frequency of the automatic frequency control system will be offset from the resonant frequency of the reference cavity to la little below said resonant freyquency, since the target frequency of the system vaccording to the present invention is the frequency at which the output signal reverses with respect to the input signal. The amount of offset can be decreased by reducing the input pulse amplitude. As a matter of fact, the amplitudes of the rpulse input signals B, D and F are greatly exaggerated in Figs. 1 and 2, as compared with i the amplitudes of the pulse frequency modulation input signals actually used in the present invention.

. detector is used there is a restricted lock-in range around the resonant` frequency of the cavity, outside of which the rectified output from the.

; plumbing is too low to operate the servo system. Therefore, a sweep circuit is incorporated so that, When'the unit is turned on, the Klystron output frequency will be swept automatically 4 through the electrical tuning range of said Klystron until it is within lock-in range.

In the servo system of the present invention, a staircase or stepwise sweep or frequency modulation orlfrequency variation of the Klystron is caused to occur, pulses for error detection and frequency control being obtained from this sweep by differentiation of the rectified output of the reference cavity which is coupled to the Klystron output.

Fig. 3 isa combined schematic and block diagram of a servo system according to this invention. To generate the sweep voltage necessary to vary the frequency of Klystron 2| in steps on the order of 500 kilocycles per step, a free-running step blocking oscillator i, running at a repetition rate on the order Aof 200,000 pulses per second, is employed. Condenser 2 is -originally step-charged from blocking oscillator lythrough avstep rectifier 3, in a direction such `that the potential of the upper plate of said condenser becomes negative with respect to thelower plate thereof, as represented by the stepped portion of the waveform in Fig. 5, which respresents the staircaser waveform of the voltage of the upper plate of condenser 2 with respect to ground under sweeping or hunting conditions. By means of lead 4, the voltage on the upper plate of condenser 2 is applied to the repeller of Klystron 2 I, so that Fig. 5 also represents the waveform of the voltage on the Klystron repeller Iwith respect to its cathode or ground under sweeping or hunting conditions. Since the step-charging of condenser 2 is in a negative direction, the stepwise or pulse frequency modulation or frequency variation of the Klystron 2l is from loW to high frequency.

By way of illustration only, to vary the voltage across condenser 2 and on the Klystron repeller by -18 volts, and to vary theY Klystron frequency -by approximately 60 megacycles, 120 steps are required from the step blocking oscillator I; the pulse output of said oscillator is therefore such that each step produces a change of 0.15 volt, which in turn causes the Klystron frequency to change 500 kilocycles per step.

A portion of the output from the controlled Klystron 2l is passed through a tuned or resonant cavity l'lhaving a frequency-output response characteristic as indicated in Fig. 6. This characteristic has the same shape as the curves A of Figs. 1 and 2 previously described, but is shown reversed and in the negative direction because this sort of a response characteristic is needed with the number of amplifier tubes used, for correct trigger polarity. Such a reversal of characteristic from those of Figs. 1 and 2 may be easily obtained by reversal of the connections of the rectifier 'l5 to which the resonant cavity output is applied. A

I When the Klystron frequency is caused to vary in `steps with time in the manner above described by means of step oscillator l, the rectified output voltage of' the cavity, whose characteristic is shown in Fig. 6, varies with time in the manner shown in Fig. 7, since the frequency sweep of the Klystronis from low to high frequency. This voltage, the waveform of which is shown in Fig. 7, is applied by means of lead 6 to the input of an amplifier 1. The voltage waveform of Fig. 7 is amplified by amplifier 1, and is applied to an RC coupling circuit, including a condenser 8 and a resistor 9.. This RC circuit 8-9 has a low timeami-'ieee ferentiating circuit to differentiate the signal applied to its input. l

The differential waveform producedA at the output'of RC circuit 8 9 is, as shown in Fig. 8, a series of pulses c and d which result from, and are produced simultaneously with, the risers a and b of the stepped Voltage wave of Fig. 7, which in turn result from, and are produced simultaneously with, the intermittent or pulsed vfrequencyv changes or modulations of the' Klystron 2I` and the intermittent voltage changes of condenser 2. Throughout the present specification, when referring to waveforms in the shape of steps, terms commonly associated with stepsV or' stairs will ordinarily be used; thus risers will" be' used to denote the vertical portions of such waveforms, while treads" will be used to denote the horizontal portions of such waveforms. It is only the changes or risers e of the stepped voltage waveform of Fig. 5 which produce the changes or risers a and b of the Fig. 'l waveform, since only the changes in the condenser voltage waveform produce changes in frequency of the Klystron 2| and changes in the output of the reference resonant cavity; between such condenser voltage changes there is no change in Klystron frequency, consequently no change in output of the resonant cavity, and therefore no pulses in the output of differentiating circuit 8 9. The output of circuit 8 9, shown in Fig. 8, consists of pulses which reverse in polarity just after the bottom ,f of the waveform of Fig. 7, since at said bottom the direction of the respective risers a and b thereof in effect reverses. Comparing Figs. 7 and 8, it may be seen that there is a reversal of polarity as between the two waveforms, that is, the positive pulses c of Fig. 8 correspond in time to the negative risers a of Fig; '7. This is -due to the fact that Fig. 7 represents the waveform of the input to amplifier 1, and amplifier 'I inverts the waveform passing therethrough; in other words, the direction of the stepped wave in the output of amplifier 1, and applied to circuit 8-9, would be the opposite of that shown in Fig. '7, with initial positive voltage risers being followed by negative risers The pulse waveform of Fig. 8, the output of circuit 8 9, is amplified and'y inverted by inverter I and then applied to the grid of an l'automatic frequency control blocking oscillator II. The grid of oscillator Il is negatively biased,

so that this oscillator is a driven or blocking oscillator.

Since the pulse waveform ofv Fig. 8 is inverted by inverter IU, the waveform applied'to'the grid `o1' oscillator H consists of a series of negative pulses followed by positive pulses, the change in polarity occurring after the bottom f of the Fig. I wave and just after the reaching by the Klystron 2 I of the resonant frequency of the reference tuned cavity "I the characteristic of whichis vshown in Fig. 6. When a positive pulse is applied to the grid of oscillator II, said oscillator is triggered to produce a high-voltage `output pulse which is applied across the primary I3 of one-shot Aan output transformer I4. The output pulse of oscillator II is inverted through a secondary winding I5 of transformer IIIA and clipped by a rectifier IB to bypass the negative backswing thereof away from the rest of the circuit connected to winding I5.

'I'he output signal pulse of oscillator II is applied through a condenser II and a rectifier I8-to charge condenser 2 in a direction opposed to the charge placed thereon by oscillator I; the amount of this opposition charge being determined by the voltage division between condensersII and 2'.. In other words, the original negative charge on` condenser 2 is reduced, thereby reducing the negative voltage with respect to ground which is applied to the Klystron repeller, causing a lowering of the output frequency of the Klystron 2l. The' voltage divisions from the oscillator II toY condenser 2 and from the oscillator I to condenser 2 are such that the` former supplies van incre*- ment of charge to said condenser which is about three times as great as the latter. Y

After the pulse supplied from oscillator II to reduce` the original negative charge on condenser 2 and to reduce the original negative'voltage appliedV to` the Klystron repeller ends, the Klystron frequency is again raised in steps as condenser 2 re"-accumulates its original' negative charge or as the voltage across said condenser is again' in'- creased in the original negative direction by means of increments of charge supplied from step oscillator I through step rectifier 3. Thus, the Klystron frequency oscillates back and forth through a small neighborhood about the reference cavity resonant frequency. Fig. 9 represents the voltage waveform on the Klystron repeller with respect to its grounded cathode under the above-described automatic frequency control conditions. The downwardly-stepped portions `g of the Waveform represent the original periodicv accumulations of negative charge on condenser 2, or the original increases of voltage across', said condenser in a negative direction, caused by. the negative increments of charge supplied to said condenser from oscillator I; during the time of these steps, the Klystron frequency is being increased in stepwise fashion. The substantially linear rising portions h of positive slope in the waveform of Fig. 9 represent the periodic reduc'- tions of the original negative charge on condenser 2, or the increases of voltage across said condenser in a positive direction, caused by the positive pulses supplied to said condenser from oscillator II; during the time of each of these linear portions the Klystron frequency is being rapidly and substantially uniformly lowered. Since oscillator II supplies a slug of charge to condenser 2-whiclr is about three times as great as that supplied thereto by oscillator I,i the change of repeller voltage caused by the linear portions h of the waveform in Fig. 9 is represented as corresponding in amplitude or height to three steps 'g of the step voltage change produced by oscillator I.

It has been stated previorsly that a sweep circuit is incorporated to sweep the Klystron frequency automatically through the electrical tuning range of the Klystron 2l until it is within the restricted lock-in range; this sweep circuit is provided by the limit blocking oscillator I9 acting with step oscillator I. Oscillator I9 allows the Klystron frequency to hunt over a range of about 130 megacycles, when it is not locked vin lthrough the servoamplier |B I. From Fig. 5, 'which represents the staircase voltage waveform on the Klystron repeller with respect to ground or its cathode under these sweeping conditions, it may be seen that when a point 18 volts below the starting voltage is reached, the Klystron repeller voltage as controlled by condenser 2 is caused to return to the starting voltage, where it again starts to step in a negative direction or down to 18 volts with respect to the starting voltage. Blocking oscillator I9 is so connected 'that Va voltage. of 18 volts acrossfcondenser-2 applied by lead 20 from the upper plate of condenser 2 to the blocking oscillator I9 will turn the tube of oscillator I9 on; when such tube conducts, a blocked oscillation is generated by oscillator I9, in such a direction as to drive the voltage of condenser 2 by means of lead 20 back to the original starting voltage to start the cycle again. Thus, in Fig. 5, the stepped portions e of the waveform represent the original negative voltage stepping of condenser 2 by step oscillator I, while the vertical portion Ic of said waveform represents the driving of condenser 2 back to the starting voltage by a blocked oscillation of limit oscillator i9. As long as the Klystron frequency is locked in through the servoamplier 6I8, what might be called the reversing of the voltage (as opposed to the original stepping of the voltage by oscillator I) is accomplished by oscillator I in the manner previously described in connection with Figs. 7 9; under these conditions the potential of the upper plate of condenser 2 never becomes sufficiently negative with respect to that of its lower plate to turn on oscillator I9', so that in the automatic frequency controlA condition oscillator I 9 remains off. Oscillator I9 operates only when the unit is turned on, to bring the Klystron frequency into lock-in range for servo operation, or in case the servoamplier 6-I 8 fails to operate for some reason.

The above provides a somewhat general description of the operation of the system. Reference will now be made to Fig. 4 for a more detailed description of the circuit and its operation.

A reflex Klystron 2! is the oscillator the frequency of which is to be stabilized or controlled by the servo system of the present invention. Such a Klystron may include a repeller electrode 22 which is connected to lead 4 of the lservoamplifier in order to apply a proper potential to said repeller electro-de, the potential applied to repeller 22 by means of lead 4 being changed by the servoamplifier to change the output frequency of Klystron 2I. .Said Klystron also includes an emissive cathode 23 which is grounded, a, control grid 2-4 biased slightly positive with respect to said cathode by means of a battery 25, and an internal resonant output cavity 26 providing two grids in the tube through which the `electrons pass, cavity 26 being biased positively a few hundred volts with respect to cathode 23 by a battery 21 to provide an accelerating voltage. Although the potential sources 25 and 21 are illustrated as separate batteries, this has been done only for purposes of simplification, the potentials for electrodes 24 and 25 preferably being obtained from the main potential source for the servoamplifier. An output loop 28 is coupled to the internal cavity 26 in order to apply the output of Klystron 2l to a coaxial transmission line 29. Said transmission line carries va portion of the Klystron output to an intermediate frequency converter crystal (not shown) and the remaining portion of said output to a waveguide 30. Waveguide 30, together with a cavity structure to be later described, provides a sampling and error detecting device.

The step blocking oscillator I includes las the main element thereof a pentode 3| having anode 32, suppressor grid 33, screen grid 34, control grid 35, and cathode 33. Anode 32 is connected through one winding 31 of a pulse transformer 38 and through a resistor 39 to a source of positive potential (not shown), on the order of 120 volts. Suppressor grid 33 is connected directly to grounded cathode 36, while screen grid 34 is connected by way of leads 46 and 4I and resistor 39 to the positive potential source, a bypass condenser 42 being provided between said screen grid and ground or cathode 36. Control grid 35 is connected through a suitable resistor 43, winding 44 of pulse transformer 38, and another resistor 45, to lead 4| and the positive potential source, to bias said control grid positively. A blocking condenser 46 is provided in the grid circuit of blocking oscillator I, the lower plate of said condenser being connected to ground and the upper plate of said condenser being connected tothe junction point of resistor -45 and winding 44.

The dots at windings 31 and 44 indicate similar polarities, and this is also true at the other transformer windings in Fig. 4. For example, if

a current flows through one winding so that the dot end is positive, the field set up in the core induces voltages in the other windings, making the dot end positive in these windings at the same time.

By means of the above-described connections, with the polarities of windings 31 and 44 as indicated, with control grid 35 connected to a posi,- tive voltage, and with blocking condenser 46 connected as indicated, no trigger pulses being applied, pentode 3l is made to operate and will operate as a free-running blocking oscillator at a rather high repetition rate, on the order of 200,000 pulses per second, such pulses or blocked oscillations being available at anode 32. As is understood by those skilled in the art, the initial voltage swing at the anode 32, when tube 3| conducts, is in the negative direction, causing the voltage -with respect to ground to drop at said anode when tube 3I conducts.

In order to provide a charge on a condenser 4'1 before tube 3I conducts and during the intervals when it does conduct, this charge being such that the upper plat-e of said condenser has a positive potential with respect to ground and the lower plate of said condenser has a negative potential with respect to ground, the upper plate of said condenser, which is connected to anode 32, is also connected through winding 31 and resistor 39 to the positive potential source; the lower plate of said condenser is connected to anode' 59 of a rectifier 5 the cathode 60 of which is connected..

by means of lead 50 to tap 52 of a dual potentiometer 5I. In order to providev an adjustable potential negative with respect to ground at tap 52. resistors 54, 53 and 56 are connected in series in that order between ground 55 and a lead 51 which is connected to a negative potential source.; tap or arm 52 engages and moves along poten'- tiometric resistor 53. A resistor 6I is connected across rectiier 5, while a bypass condenser 58 is connected between arm 50 or tap 52 and ground. 'l

Assuming for purposes of `illustration that. 52 is located at such a point that the potential at said tap is negative volts with respect to ground and that the potential of the positive source is volts, the condenser d1 is charged to a voltage of 220 volts during non-conduction of tube 3l through a circuit traced as follows: positive side of the positive source,resistor 39, Winding 31, condenser 41, anode 59 and cathode 66 of recti-A fier 5, negative tap 52 of potentiometer 5I, the positive side or ground of said potentiometer, and thel grounded or negative side of the positive source. Since the voltage between potentiometer tap 52 and ground and the voltage of the positive source are connected in series aiding in this circuit, the voltage across condenser 41 is the sum of these two voltages and the upper plate of contap l denser- 41 ,hasapotential of +120 voltswith respect to ground and the lower, plate of said condenser has a potential of -100 voltswith respect-to ground.

, A -parallel circuit to the one already described is provided betweenthe lower plate of condenser 41 and tap 52, this circuit including in series, from said plate of said condenser, the cathode 48. of rectier 3, the anode 49 of said rectier, the main condenser 2, and lead 50.

When tube 3| conducts in accordance with the blocking Oscillator operation of the circuit I, its;

anode voltage with respect to ground or cathode' 36..decreases substantially instantaneously, and for the purposesof the present discussion it mayV be -assumed that this decrease amounts to 60 volts. At .the instant of conduction in tube` 3|, its' anode voltage with respect to ground and also the voltage on the upper plate of condenser 41 with respect to ground drop to +60 volts from their original. +120 volts. Since the charge on condenser 41 cannot change instantaneously, at said instant of conduction the-lower plate of condenser 41 follows in potential the upper plate,

also dropping 60 volts and reaching a potential oi 160 volts with respect to ground. This 160 volt absolute potential is more negative than the -100 volt absolute potential yof tap 52, which means that the cathode 48 of rectier 3 is negative with respect to its anode 49 by some 60 volts, a condition permitting conduction in said rectier. During `the original pulse of blocking oscillator then, while tubev 3| is conducting and while' its anode is +60 volts with respect to its cathode or ground, condenser 41 partially discharges through tube 3|, ground, resistor 54, part of resistor 53, Vlea'd'5|l,`condenser 2, and rectifier 3,'juntil the lower plate of condenser 41 reaches approximately the potential of tap 52,'which is 100 volts with respect to ground. When it does so; discharge of condenser 41 stops because at such time the cathode 48 of rectifier 3 willno longer be negative with respect to its anode 4S. During this time of discharge while tube 3|Y is conducting, the anode 59 of rectier 5, connected to the lower plate of condenser 41, is negative with respect to its cathode, connected to lead50, so that said rectier cannot conduct.` Throughout the present specification, the phrase absolute po tential or absolute voltage of an element means the 'potential or-voltage of such element with re*- spect to ground.

vDuring the timeV of this partial discharge of condenser A41 vto `a` Voltagek of approximatelyV v160 volts thereacross (its upper plate remaining at an Y..

absolute potential of +60 volts and its lower plate 'going to an absolute potential of approximately 100 volts), condenser '2 is charged, in such a direct-ion that its upper-plate goes negative 'with respect to itslower plate, toa-small voltage, on the order of- 0.15 volt for example, this voltage change across condenser 2 being de'- termined by the relation between the capacitances orV condensers -41 and 2 and being much smaller than'the change of the voltage across condenser 41A because the capacitance of condenser 2 is verylarge compared tothe capacitance of` condenser 41. Thus, a small increment of charge is supplied to lcondenser 2 for or during each successive pulseof oscillator i; in this way, condenser 2 is step-charged with "its upper plate negative with respect to its' lower plate in response to thev operation of oscillator Wlien'tube 3l' is rcut off because'of'the block-V ing'acti'onfof condenser V45'this cutof 'of said tube-,being rsubstantially instantaneous, the ab soluteyoltage ofanode 32 or the upper plate .of

condenser 41 ,instantaneously returns to +120 volts, the voltage ofthe positive potential source. Thus, .the absolute potential `of said upper plate rises 60 volts, and, since this change occurs substantially instantaneously and the charge on condenser 41 cannot change instantaneously, the.

absolute potential of the lower-plate of condenser 41 also rises 60 volts at this instant, from. ap-

proximately Volts with respect to ground` pulses, condenser 41 recharges through its original, charging circuit to substantially its original valueof charge, .tube 3| being non-conducting or cut` oiT during. this time. Condenser 41 is recharged toa voltage of substantially 220 volts thereacross, the absolute potential-of its upper plate aty the.

end of this charging period .being -volts and the absolute potential of its .lower plate at this time being .-100 .volts..When vcondenser L41 is` so. charged, the chargingthereof, stops -becauseat such time the cathode 60 .of rectifier 5 will no longer .benegative with respect to its anode..59.- During this timeof recharging of condenserV 41. while tube.3| -is cut .off or in vthe non-conf.

ducting condition, .the` cathode 48 ofl rectifier. 3, connected tothe lower .fplate of condenser .41,

is` positive with respect to its anode, connected to. condenser 2` and `leadlLso that said rectier cannot conduct. Also, since condenser 2 .is

charged during the pulses of blocking oscillator. in such a direction .thatits upper. plate becomes negative withrespect toits lowervplate, the potential` applied toY the. cathode 48 vof rectiei 3 from `the lower plate of .condenser 2 through resistor 6| is positive withrespect to. the Voltage applied directly from the-upper plate of lcondenser V2..,tothe anode 49A of said rectifier, so.`

that .said rectifier cannot conduct to discharge condenser- 2. Therefore, i the increments of charge supplied vto condenser-2 during yeach pulse of. oscillator orduring each time of conduction of tube 3| `are trapped .thereornso that condenser 2 is charged in al stepwise manner by the operation ,of blocking A-oscillator with its upper plate goingnegatiVe withrespect to its lower plate. The upper plate of condenser l2 is connected, by means of Aleads 20 and 4,4 directly to repeller 22 of controlled Klystron 2|, in order torapply the absolute potential of said upper plate or Vthe Voltage ofi said upper plate. with respect to. ground, asvacontrolling potential on repeller 22 with respectto the .grounded cathode.

23.. Avpredetermined vbias voltage is provided onrepeller 22 through condenser 2 by lead. 50

`from tap 52', since .the lower plate of said condenser is connected directly toY lead 50;. the ,voltageat tap .52. is negative .with respect to ground so that anegative bias with respect togrounded cathode. 23 is. provided on repeller 22 by means,

ofi the above-described. connection. An adjustablepotentialnegative with ,respect to ground 55 or Klystron cathode 23 is provided through conrepeller negatively with respect to cathode 23.A .Sincethe said bias voltage -is negative with rev-`A eration of a reex Klystron requires thaty the repeller voltage with respect to the cathode be negative at all times. y The step increases e in the negative direction of the absolute potential on the upper plate of condenser 2, such absolute potential being applied to repeller 22, cause the output frequency oi Klystron 2i to sweep in a stepwise manner from a low to a high value.

It is advantageous to provide a linear staircasecharging of condenser 2 by the operation of oscillator I, to make all the risers e in Fig. 5 of substantially equal height. This linear charging, rather than exponential charging, is desirable, and may be accomplished by applying to the condenser constant current pulses rather than constant voltage pulses, since the latter provide exponential charging of said condenser because of the opposing voltage across said condenser as the charge on the condenser increases. This invention contemplates and accomplishes staircase charging of condenser V2 or staircase variation of the voltage across said condenser from a source of substantially constant current pulses. plate characteristicssuch that, for each value of control grid voltage, the plate voltage-plate current curve has a portion of substantially con- 12 and cathode 65. Cathode 65 is connected direct-I ly to the upper plate of main condenser 2, so that the potential on this plate is applied at all times directly to said cathode.v Grid 64 is connected through one winding 66 of a pulse transformer 61 to a lead 68 which is in turn connected to a movable arm or tap 69 of potentiometer 5|. Arms 52 and 69 are mechanically. coupled together, as indicated, so that they move together. The potentiometric resistor 'I0 which arm 69 engages has one end connected through resistor 'Il -l winding 13.

Tube 3| is a vpentode and therefore has stant positive slope and a portion of substantially Y zero slope. The latter portion is known as the constant current portion of the pentode characteristic. Y

According to this invention, blocking oscillator pentode 3| is so operated as to in effect supply constant current increments to condenser 2 each time said tube conducts by means of the discharge circuit for condenser III as previously described. When tube 3| generates a blocked oscillation, grid current flows therein because the grid 35 of said tube is driven positive by the plate voltage change. The resistance of resistor 63 is large compared to the grid-cathode resistance of' approximately 1,000 ohms which exists when grid current is drawn in almost all vacuum tubes. The resistor 43 and the grid-cathode resistance of tube 3| provide 'a voltage divider. Since resistor 43 has a rather high resistance, the ilow of grid current in tube 3| is limited, thus limitingr the positive voltage on the grid 35 with respect to ground during conduction in tube 3|. The said positive grid voltage is limited to a value such; that, pentode 3| is limited to a constant current region for the plate voltage thereon and does not. reach the region of positive yslope in its plate characteristic grid-voltage family for said plate voltage, which it would do if the positive absolute voltage on the grid were not s0 limited but were allowed to increase. By so limiting pentode 3| to its constant current region during conduction, it inV effect provides a constant current discharge circuit for condenser 41 each time it conducts. thus providing increments of constant current to condenser 2 to produce linear staircase or stepwise charging of condenser 2.

' The limit blocking oscillator I 9 will next be described. Oscillator I9 includes, as the main element thereof, a triode 62 having anode 63, grid 64.

to ground 55 and its opposite end connected to lead 51, which is connected to a negative potential source. In this way, a negative bias potential with respect to ground is applied to control grid 64, said grid of tube 62 being biased to a point that requires a relatively large negative voltage with respect to ground applied to cathode to turn on'tube 62. A bypass condenser 12 is connected between leads 56 and 68.

vAnode 63 is connected through a winding 'I3 of transformer 61 to the lower plates of condenser 2, a small condenser 'I4 being connected across therefore the anode-cathode voltage of tube v62. The -18 Volts appliedto cathode 65 necessary to turn on tube 62, means that when condenser 2 is charged to -18 volts so that its upper plate or the cathode 65 has a potential of -18 volts with respect to its lower plate or the anode 63, tube 62 will conduct, but when condenser 2 is charged to less than -18 volts, tube 62 will not conduct. Taps 52 and 69 of the dual potentiometer 5| are` mechanically coupled togetherin such a way that the potential of tap 69 applied to grid 64 will at all times, throughout the range of movement of said taps for variation of thev bias on repeller 22, be negative, with respect to that applied by tap 52 to the lower plate of condenser 2 and said repeller, by an amount just slightly less than the algebraic sum of the -18 volt ligure selected and the cutoi voltage of tube 62 with 18 volts applied between the anode 63 and the cathode 65. In this way, it is assured that when a potential of 18 volts across condenser 2 is reached, during the charging thereof by the operation of oscillator I, tube 62 will conduct.

Condenser 2 is, in eiilect, the blocking condenser for blocking oscillator I9, this condenser being in the cathode circuit of this limit blocking oscillator and serving as a cathode blocking condenser, rather than this oscillator being provided with a grid blocking condenser as in other blocking oscillators. When tube 62 conducts, at the end of the sweep, or when the voltage across condenser 2 reaches 18 volts, there is an excess of electrons on the upper plate of condenser 2, since at this timethe yupper plate of said condenser is at a potential of 18 volts relative to the lower plate.

thereof. When tube 62 conducts, electrons are l drawn off the vupper plate kof condenser 2 by drawing them from the cathode 65 which is connected to said upper plate, causing the upper plate of condenser 2 -to go back in a positive direction, discharging said condenser. Thus, the

negative voltage sweep or charging of condenser 2V The voltage across condenser 2 isv 13 duced'by the charging of said condenser by the operation of step blocking oscillator I, while the substantially vertical increase, in a positive direca tion, of said absolute upper plate voltage as at k (when the voltage across the condenser has reached 18 volts) is produced by the discharging of said condenser 2, by limit blocking oscillator I9, in the manner just described. rIube 62 remains cut off, and blocking oscillator I9 remains blocked, until the voltage across condenser 2 lagain reaches -18 volts at the end of the next staircase sweep of said voltage by the operation of step oscillator I, at which time tube 62 again conducts because of the sufficiency of the anodecathode voltage thereon, the grid bias permitting Y conduction under these voltage conditions; when tube 62 conducts, condenser 2 again is discharged. These voltage variations during the hunting orsweeping condition cause staircase-sweep fre- `quency modulation of the Klystron output frequency from low to high frequency, followed by almost instantaneous return of said Klystron output frequency from high to low frequency.

Waveguide 30 has coupled thereto, intermediate its ends, a resonant cavity 15 which may, for example, be a circular cylindrical cavity resonating in the TE1,1,1 mode. Said cavity serves vas a reference standard of frequency, providing a bandrass filter having an output voltage-fre'- quency response characteristic of the slope generally shown in Fig. 6, which is similar to the conventional curve for a singly resonant circuit. A crystal detector 15 is also coupled to waveguide '30, at the output side of the filter 15, the pilot signal from local oscillator 2i being fed into the *t* 'input of filter 1'5 by transmission `line 29 and waveguide 39, as previously described.

YThe rectined modulation signal of the output of the waveguide and cavity structure appears at the output leads 6 of crystal detector 16. When the Klystron output frequency is caused to vary in steps by the operation of step oscillator I in the manner previously described, the curve of Fig. 6 appears on a time scale as shown in Fig. '7. The waveform curve of Fig. '7 represents, therefore, the waveform of the voltage produced between leads 6.

One of the leads 6 is connected to ground 55, while the other is connected though a coupling condenser 11 to the control grid 18 of the pentode 19 'which serves as the amplifier stage 1. -A leak resistor 80 is connected between control `g-rid 18 and grounded cathode 8| of pentode 19.' Suppressor grid 82 of tube 'I9 is connected to 4"cathode 8I. Screen grid 83 of said tube is connected through a resistor 84 to a source of positive Potential on the order of 120 volts, aubypass `condenser 85 being connected between grid 83 4and ground 55 or cathodel. Anode 86 of tube 19 is connected through apair of resistors 81 and 8 8 to a source o f positive potential, not shown, on the order of 1'20 volts. By means of the aforesaid connections, pentode 19 operates as an amplifier to amplify the voltage wave of Fig. 7 which is the input to said amplifier, tube I9 also functioning to invert the input signal thereto. In order to couple the output of amplifier 1 to the inverter Iii, anode 85 is connected through a coupling condenser 8 having a low capacitance to the control grid 8 9 of an amplifier and inverter pentode 99, the coupling circuit being completed b'y a'l'ealk resistor 9 connected between grid 8S and ground 55. The RC couplingcircuit 8 9 'has a .low time-constant, such that said circuit acts tozdi-ierentiate. the signal applied to its ir!-v The differentiated waveform, the output of coupling circuit 8 9 or the input signal of amplier and inverter stage I0, has the shape shown in Fig. 8, it being remembered that the input signal to circuit. 8 9 has a waveform of the same character as that shown in Fig. 7 but inverted with respect thereto. Due to the differentiating action of circuit 8 9, a steep impulse is produced in ":he output of said circuit simultaneously with .each of the risers a and b in the stepped waveform of Fig. 7, since during these risers the time rate of change of the input voltage of circuit 8 9 is very large, While during the treads of the stes the time rate of change of the input voltage of said circuit is substantially zero. The output pulses of circuit 8 9 therefore coincide in time with corresponding risers in the steps of Fig. '7. The initial pulses c of Fig. 8 are in a posi'ive direftion, since the initial risers in the input wave to circuit 8 9 are in a positive direction, the inverse of Fig. '7. The polarity of the output pulses of circuit 8 9 reverses at or im.- mediately after the time of the bottom f of the Fig. 7 wave, since at this time the direction of the risers of Fig. 7 reverses, Ymaking negative risers at the input of circuit 8 9 and consequent negative pulses d at the output of said circuit simultaneously with such negative risers.

From a comrarison of Figs. 6 and 7, it may be seen that the bottom f of the wave of Fig. '7, or the reversal of the direction of the risers a andb thereof, occurs when the resonant frequency of the reference cavity 15 is reached by the stepfrequency-modulateld Klystron 2l. Since this is so, the reversal of polarity of the Youtput pulses of circuit 8 9 occurs simultaneously with the reaching of the resonant frequency of cavity 15 by the Klystron 2 I. Thus, pulses for error detection are obtained by dierentiation of the rectified output of cavity '15, the polarity of these pulses indicating the direction of error from the target frequency or resonant frequency of reference cavity 15.

The servoarnplier is inherently low-microphonic. Because of the low time-constant. of circuit 8 9 in the grid circuit of the second amplif'ier tube 9.0, frequencies in the microphonic range are considerably attenuated.

The pentode 99 of the amplifier and inverter stage Iii includes, in addition to control grid 89, an anode 9i, a surpressor grid 92 connected to grounded cathode 93, and a screengrid .94 cone nected to the positive` potential source through resistor 84. Anode 9I is connectedthrough a resistor to resistor 88 and the source of positive lplae potential.4 A bypass condenser 95 is connected between the junction of resistors 88 and 95 and ground '55. Pentode. 90 functionsto amplify and invert the input pulses c andd of Fig. 8 applied thereto, to providein the output of. said pentode negative imnulses followed bypositive impulses, the positive impulses occurring after the resonant frequency of reference cavity 15 has been reached.

In order to couple the output of amplifier and inverter stage I0 t0 the automatic frequency control blocking oscillator I I, anode 9| .is connected through a coupling condenser 9'! .to the control grid 98 of a triode SS which constitutes the heart of the driven or one-shot blocking oscillator II. In order to bias grid 98 negativelyV with respect to grounded cathode |91, to provide the desired one-shot actionfor tube 99, a pair of resistors IUI and, i582 are' connected miserias. between erQund 55 and negative lead 51 to provide a voltage divider; the common junction of these two resistors is connected through a grid resistor |09 to grid 98. A bypass condenser |03 is connected across resistor I I, the interwinding capacity of transformer I4 providing the blocking capacitance for blocking oscillator I I. Anode |09 of triode 99 is connected through a winding I3 of blocking-oscillator transformer I4 and through a resistor |05 to the positive potential source, a bypass co-ndenser |96 being connected between ground and the junction between resistor |05 and winding I3.

Blocking oscillator triode 99 is connected so that the feedback winding of transformer I4 is in the cathode circuit, the grid 98 not being connected directly to the transformer; to carry out this purpose, cathode |01 is connected through winding I08of transformer I4 to ground at |99. Thus, during the trigger period, before tube 99 goes into a blocked oscillation, the grid 98 has a sufficiently high negative bias to cut olf the tube and thus the grid circuit presents a high impedance to the previous plate 9|, resistor |00 having a high impedance, permitting the use of high enough plate impedance in tube 90 to develop considerable amplification. Therefore, blocking oscillator I I can be triggered directly from a high-impedance source without a trigger tube.

Transformer Ill is a special blocking oscillator transformer particularly adapted to this type of operation. The turns ratio from plate to cathode to output winding I5 is 3:1 :1.5, and approxmiately the same amplitude pulse is developed across each winding because of capacitive coupling and possibly because of saturation eects. The coils are Wound for minimum capacity to each other.

A clamping diode rectifier I2 has its cathode I I0 connected to grid 98 and its anode I I I connected to the ungrounded side of resistor IOI. Grid 98 is negatively biased, as stated above, so that tube 99 is normally off or non-conducting. When the grid 98 is triggered in a positive direction by a positive pulse appearing in the output of stage I0, tube 99 conducts, the voltage of plate |04 goes in the negative direction, and a voltage is induced in cathode winding |08 driving cathode I0'I negative, which is in a regenerative direction.

Without rectifier I2, grid 98 is tied to a highimpedance circuit, since resistor |09 has a high impedance. The grid-cathode resistance of tube 99, when the cathode |01 becomes negative and grid current is drawn, is low, and the circuit impedance of the cathode is low. rhus, the grid 98 is driven -by the cathode circuit, and becomes almost as negative as the cathode. Because the grid 98 is then not very positive with respect to the cathode |01, the plate current through tube 99 is not very high, and the output pulse at output transformer winding I5 is unsatisfactory in voltage amplitude.

' 'Howeven with rectier I2 connected as disclosed, grid 98 is no longer tied to a high-impedance circuit when grid current is drawn, since when grid current iiows the electron flow is from cathode |01 to grid 98, cathode IIO, anode II I, to ground and back to cathode |01. Rectifier I2 will conduct when electron ow is in this direction, 'and the impedance of said rectifier is very low when the same conducts, providing therefore substantially a short-circuit across resistor |00; as a result, under these conditions grid 98 has a low externa1 circuit impedance when grid current is drawn. Due to this low external circuit impedance, grid 98'is clamped by rectifier I2. Thus, 'large grid current can flow and grid 98 is no longer driven by the' cathode circuit but can remain very positive with respect to cathode |01 as said cathode is driven negative. Heavy pulse current then flows in tube 99 as a result of this large positive grid voltage with respect to the cathode, approximately Volts bein-g developed across the load with a -volt plate supply during the blocked oscillation generated.

Tube 99 is operated near cuto so that only the positive-going portion of the pulse output signal of stage i9 causes said tube to be triggered. As described above, the positive pulses occur after the resonant frequency of reference cavity 75 has been reached. The additional negative voltage provided on the grid 98 of tube 99 by the charging of condenser |93 when blocking oscillator II generates a blocked oscillation is such that any positive pips or pulses that come through amplier I0 within a short interval after atrigger pip, before condenser |03 discharges through resistor IIII, have no eifect. Thus, there is no likelihood of tube 99 generating free-running pulses. It will trigger only immediately after a pulse of step oscillator I, which latter pulse operates to vary the charge on condenser 2, the voltage on repeller 22, and the output frequency of Klystron 2|, vthis Variation of Klystron output frequency resulting in a positive pulse to trigger oscillator II if the Klystron output frequency is above the resonant frequency of reference cavity '15, and in a negative pulse if the Klystron output frequency is below said resonant frequency.

Secondary winding I5 of blocking oscillator transformer I4 is connected as indicated by the dots adjacent windings I3 and I5. The upper end of winding vI5 is connected through a condenser |'i to the anode |I2 of a diode rectifier I8 the cathode ||3 of which is connected to the lead 20 and the upper plate of main condenser 2. The lower end of winding I5 is connected to negative potential lead 98. A diode rectifier I6 has its cathode Il!! connected to the common junction of condenser I'I and anode |I2, and its anode I I5 connected to lead 68 and the lower end of winding I5. A resistor I I5 is connected across rectier IS. Rectifier I6 functions as a clipper to remove or bypass the negative back-swing of the output pulse of oscillator II, which appears across winding I5, away from the remainder `of the output circuit including rectifier I8 and condenser 2, and also to discharge condenser I'I after a pulse of oscillator II, since after such pulse the left-hand plate of said condenser, or anode II5, -is positiveA with respect to the right-hand plate of said condenser, or cathode I I4, and since after such pulse the lower end of winding I5 returns,y to the absolute potential established by tap 69. Here, the term negative means that the upper end of winding I5 is negative with respect to its lowerend. Under these conditions, cathode IM of rectier I9 is negative with respect to its anode I I5 and said rectifier conducts.

As previously stated, the potential of tap.69 is at all times negative with respect to vthat of tap 52. Lead 98, connected to tap 69, therefore applies a potential, through resistor IIS to the anode H2 of rectifier I8, which is negative with respect to that applied by lead 50 from tapl 52 through condenser 2 to the cathode I|3 of said rectier. Thus, rectifier I8 is biased with its anode negative with respect to its cathode, so that it will present a high-resistancevvdirect current lpath to the step charge on main condenser 2, Vin which the upper plate of condenser and y 17 cathode II3 areLnegativewithmespect'to the lower plate .of said condenser.

Condensers Il and 2 function as a capacitancetype 'voltage divider. The Voltage of the vpulse developed across the load b y oscillator Il is suflicient to Vovercome 'the bia-s on rectier `I8 and charge condenser 2 in a direction the reverse of the step charge by an amount determined by the voltage division between condensers Il `and 2. In other words, the'output pulse generated by blocking oscillator II when it is triggered is applied through condenser I'I and rectifier I8 to reduce the step charge on main capacitor 2, this step charge having been placed .thereon by .the action of step blocking oscillator I in the `manner previously described. .This reduction of the step charge on condenser 2 reduces the negativevvoltage applied to the Klystronrepeller 22 and causes the output frequency of the Klystron 2.I .to be lowered. The circuit from the winding I5, across which the generatedpulse appears, to condenser 2, may be traced as follows: upper end of winding Icondenser I?, anode II2 and cathode II3 ofrectiiier I3, condenser 2, lead 59, condenser l2, and lead 58, to thelower end of Awinding I5, the condenser l2 normally `being charged to a Voltage vequal to the potential diiierence between leads 59 and 68.

The voltage .division from the automatic-frequency control blocking oscillator I I to condenser 2 and that from the stepblocking oscillator I to condenser -2 are such that the former supplies aslug of charge about three times as great as the latter. When .the pulse from transformer I4 ends, the Klystron frequency is again raisedvin steps condenser 2 accumulates astep charge from .oscillator I through rectier 3. Since Ain the stepwise sweep of the charge on rthe upper plate of condenser 2 Vnegatively with respect to ground or the staircase sweep of the Klystron 2I ,from low to highfrequency by step oscillator I, p ostive pulses are produced in the output of circuit 8- afterthe resonant frequency of reference cavity 'l5 .has been reached and simultaneously with the .frequency changes of Klystron 2|, since .positive pulses trigger theautomatic frequency control blocking ,oscillator I I to reduce the step charge on condenser 2, and sinceoscillater .IIsupplies a slug of charge to condenser 2 about three times as-great as that .supplied thereto by oscillator I, thewaveiormof the voltage with respect to ground Aon the Klystron repeller is as shown in Fig. 9, and the Klystron frequencyzoscillates about the resonant lfrequency o"fcavity l5. :In other words, when the `servoamplinervE-I'B is in operation or when the system is in the automatic frequency control condition, the Waveform of the voltage with respect .to ground on Klystron repeller v22is as shownin Fig. 9, in which the downwardly-stepped portions g represent the-periodic Vaccumulations of charge on condenser 2 produced bythe operation ofstep oscillator I and in which ythersubstantially linear rising portions h of positive-slope represent the periodic reductions of charge on said condenser caused by the supply .of'corresponding positive pulses to said condenser from oscillator I I. Duringthe timeof the steps g in Fig. 9, theKlystron frequency is Vbeing increased in stepwise fashion, while during the time of the positively-sloping is lowered.

The limit blocking. oscillator Ill-"operates in the manner previously described vtofcausefhunting of the absolute, potential of nthe .upper plate of won'- denser 52 and .of V,the Klystron lfrequency Lover ga. ratherjwide range rwhich includes the ,look-,in range `of zthe -servoampliiier ,I 8., .when the Kly stron frequency is -not locked in through servoaniplier .for -soine ,-reason.

' LThe Iservo system .of -this invention :not only supplies error liiniiorniation,-in the lform of pulses,v as illustrated in Fig. 8, but correction is by means of pulses The two -ainpliiier stages fl and -IU feed'blockingbscillator II and asflong as fthe positive .pulsefatthe `input to oscillator I I ,is sufficient .togtrigger the same, the system is insensif; tive toiany @further:changeinv amplitude, whether it be'due-to'degree of error .or to vmodulation;o,i the signaliat-microphonicfrequency. 1 The mechanism of frequency .correction is as follows: If'rthe Klystron,outputireguency is ,be.- low the;resonant frequency of ,reference cavity l5, the staircasegsweep .drives the Klystron frequency in .the correct fdirection. Correction takes; placezat about. 5.00.Y kilocycles per ,iivefmicro-f second step, :or -,one; megac.yc1e in ten Mmicroseconds. ,If the VKlystron frequency above the resonant Airequencv :of the :reierence gcavity, but Within ,lock-in rangethen for ,each ,slug .ofzcharge from the action :onstepfblocking oscillator :I 4.into condenser 2, I. driring Ythe Klystron frequency one step higher, ,the fautomatic ifrequencypontrol blocking. oscillator VH :charges .condenser 2 z thnee timesas much inzthe.opposite.directiongtsinceor each such f; slugjrom V.oscillator .I a positive :pulse is Y; produced :which t triggers oscillator il; I. 'lims, with each pulse ,of thelistep .blocking oscillaton the `zKlystron; frequencyimovesiin therorrectcdirection 3.-1 )500:1009 gkc.,.zuntil ,it :is back in theneighborhoodpi ,thecorrectfrequency. .fjCorrection thus I takesi placeat.l about 10,00 .kilocycles per ve-microsecond step, or one niegacycle in ve microseconds. If .tor ...some reason :the Klystron frequency `isabove the resonantrfre.- quency but outsidelock-innrange, it Ewill step itc the highest g frequency, where the; limit blocking oscillator `I9 triggers nii, and the Klystronzfre-f cuency returns ito `the lowest value, whence :it steps to -the correctfreqnency,al1'withinzabont 600 microseconds. i :The-high frequency:.of;operation of'this system makes .it L possible :to lcorrect :satisfactorily rior frequency imodulation adue to :Vibration of zthe Klystronaelementszor i due` to:power:supplyrippla It also reduces .thepeiiects tof; leakage from com denser 2, and makes it-.possiblelxto use arsmaller condenser pin this location. Inf fact, one of @the main advantages 4oi my invention :is 1thatzthere arejnot very manyrcondensersfof large capacity used in the entire system. i Due to the use;of'a.diierentiating circuitnin thepresent =systeni,1which produces pulses oigop-l posite lpolarities above f and below the' resonant frequency of the; system, the'V output of the error detector itself, which. is;.illustrated in` Fig. `'1,-fneed not have, sense. o s, Of course,-it:is tofbezunderstood thatithisginvention is notv limited -to :the-particular: detailsra's described above, `as many equivalents Willasugggestthemselves tothose skilled in theart. Flor example, since the servosystemof this invent-ion is Well adapted `for vfrequencyfjstabilization, it can .control frequency V,by ,controlling areactanoe or resistance`.tube, -or V by :controlling :voltage in any; system Vof "which the frequency iszariunction of: a zvoltage. The .control of i .the output ire',-V quency ofia Klystron-eoscillator ;by; controlfofsits repellerivoltagexhastbeen;describedhereinzmerely ibyrwayxnf iexainple. :.Theflsystemcof :this innen',-

tion can be used to control other quantities than frequency if the error detector response has the form of a resonance curve. Various other variations Will suggest themselves. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of this invention within the art.

' What is claimed is:

1. A servo system, comprising a condenser, means for charging said condenser in a stepwise manner with a predetermined polarity, means responsive to changes in potential of said condenser for deriving simultaneously with such changes pulses of a polarity which reverses when a desired condition is reached by a controlled device, and means actuated by a pulse of said reverse polarity for reducing the charge of said predetermined polarity on said condenser.

2. A servo system, comprising a condenser, means for charging said condenser in a stepwise manner with a predetermined polarity, means responsive to changes in potential of said condenser for deriving simultaneously with such changes pulses of a polarity which reverses when a desired condition is reached by a controlled device, means responsive to a pulse of said reverse polarity for producing an output voltage pulse having a polarity opposite to said predetermined polarity, and means for applying said output pulse to said condenser to reduce the charge of said predetermined polarity thereon.

3. A servo system, comprising a condenser, means for charging said condenser in a stepwise manner with a predetermined polarity, means responsive tov changes in potential of said condenser for deriving simultaneously with such changes pulses of a polarity which reverses when a. desired condition is reached by a controlled device, means responsive to a pulse of said reverse polarity for producing an output voltage pulse having a polarity opposite to said predetermined polarity, and means for applying said output pulse to said condenser to reduce the charge of said predetermined polarity thereon, said output pulse having an amplitude several times that of each of said repetitive pulses.

"4.1A servo system, comprising a condenser, means for charging said condenser in a stepwise manner with a predetermined polarity Yfrom a predetermined state` of charge, means responsive to a predetermined condenser voltage for producing an output voltage pulse having a polarity opposite to said predetermined polarity, and means for applying said output pulse to said condenser to return said condenser to said state of charge.

45. A servo system, comprising a condenser, means for charging said condenser in a stepwise manner with a predetermined polarity from a predetermined state of charge, means responsive to alpredetermined eondenservoltage for producing an output voltage pulse having a polarity opposite to said predetermined polarity,'and means for applying said output pulse to said condenser to return said condenser to said state of charge, said output pulse having an amplitude many times that of each of said repetitive pulses.

' 6. VA servo system, comprising a condenser, means for charging said condenser in a stepwise manner with a predetermined polarity from a predetermined stage of charge, means responsive to changes in potential of said condenser for deriving simultaneously with such changes pulses of a polarity which reverses when a desired condition isreached by Y.a controlled device, means 2U actuated by a pulse of said reverse polarity for reducing the charge of said predetermined polarity on said condenser, and means responsive to an excessive condenser Voltage of said predetermined polarity, due to the failure of the chargereducing means to operate, to return said condenser to said state of charge.

7. A servo system, comprising a condenser, means for charging said condenser in a stepwise manner with a predetermined polarity from a predetermined state of charge, means responsive to changes in potential of said condenser for deriving simultaneously with such changes pulses of a polarity which reverses when a desired condition is reached by a controlled device, means responsive to a pulse of said reverse polarity for producing an output voltage pulse having a polarity opposite to said predetermined polarity. means for applying said output pulse to said condenser to reduce the lcharge of said predetermined polarity thereon, and means responsive to an excessive condenser voltage of said predetermined polarity, due to the failure of the charge-reducing means to operate, to return said condenser to said state of charge.

8. A servo system, comprising a condenser, means for charging said condenser in a stepwise manner with a predetermined polarity from a predetermined state of charge, means responsive to changes in potential of said condenser for deriving simultaneously with such changes pulses of a polarity which reverses when a desired condition is reached by a controlled device, means actuated by a pulse of said reverse polarity for reducing the charge of said predetermined polarity on said condenser, means responsive to a predetermined excessive condenser voltage of said predetermined polarity, due to the failure of the charge-reducing means to operate, for producing an output voltage pulse having a polarity opposite to said predetermined polarity, and means for applying said output pulse to said condenser to return said condenser to said state of charge.

9. A servo system, comprising a condenser, means for charging said condenser in a stepwise manner with a predetermined polarity from a predetermined state of charge, means responsive to changes in potential of said condenser for deriving simultaneously with such changes pulses of a polarity which reverses when a desired conditionis reached by a controlled device, means responsive to a pulse of said reverse polarity for producing an output Voltage pulse having a polarity opposite to said predetermined polarity, means for applying said output pulse to said condenser to reduce the charge of said predetermined polarity thereon, means responsive to a predetermined excessive condenser voltage of said predetermined polarity, due to the failure of the charge-reducing means to operate, for producing an output voltage pulse having a polarity opposite to said predetermined polarity, and means for applying said last-named output pulse to said condenser to return said condenser to said state of charge.

l0. A frequency-control system, comprising an oscillator the output frequency of which is variable in response to variation of a control voltage, a condenser the voltage on which provides said lcontrol voltage, means for charging said condens-v er in a stepwise manner with a predetermined pochanges pulses of a polarity which reverses when said output frequency reaches a predetermined value, and means actuated by a pulse of said re- Verse polarity for reducing the charge of said predetermined polarity on said condenser, to thereby change said output frequency in a direction opposite to said predetermined direction.

l1. A frequency-control system, comprising an oscillator the output frequency of which is variable in response to variation of a control voltage, a condenser the volt-age on which provides said control voltage, means for charging said condenser in a stepwise manner with a predetermined polarity to correspondingly change said output frequency in a predetermined direction during each of said steps, means responsive to said output frequency for deriving simultaneously with such changes pulses of a polarity which reverses when said output frequency reaches a predetermined value, and means actuated by a pulse of said reverse polarity for reducing the charge of said predetermined polarity on said condenser, to thereby change said output frequency in a direction opposite to said predetermined direction, the amount of said last-mentioned frequency change being several times greater than the amount of each of said rstmentioned frequency changes.

12. A frequency-control system, comprising an oscillator' the output frequency of which is variable in response to variation of a control voltage, a condenser the voltage on which provides said control voltage, means for charging said condenser in a stepwise manner with a predetermined polarity from a predetermined state of charge to correspondingly change said output frequency in a predetermined direction during each of said steps, means responsive to a predetermined condenser voltage for producing an output voltage pulse having a polarity opposite to said predetermined polarity, and means for applying said output pulse to said condenser to return said condenser to said state of charge, to thereby change said output frequency in a direction opposite to said predetermined direction.

13. A frequency-control system, comprising an oscillator the output frequency of which is variable in response to variation of a control voltage,

a condenser the voltage on which provides said control voltage, means for charging said condenser in a stepwise manner with a predetermined polarity from a predetermined state of charge to correspondingly change said output frequency in a predetermined direction during each of said steps, means responsive to a predetermined condenser voltage for producing an output voltage pulse having a polarity opposite to said predetermined polarity, and means for applying said output pulse to said condenser to return said condenser to said state of charge, to thereby change said output frequency in a direction opposite to said predetermined direction, the amount. of said last-mentioned frequency change being many times greater than the amount of each of said first-mentioned frequency changes.

14. A frequency-control system, comprising an oscillator the output frequency of which is variable in response to variation of a control voltage, a condenser the voltage on which provides said control voltage, means for charging said condenser in a stepwise manner with a predetermined polarity from a predetermined state of charge to correspondingly change said output 22 frequency in a predetermined direction during each of said steps, means responsive to said cutput frequency for deriving simultaneously with such changes pulses of a, polarity which reverses when said output frequency reaches a predetermined value, means actuated by a pulse of said reverse polarity for reducing the charge of said l ,determined polarity on said condenser, to reby change said output frequency in a direction op vite to said predetermined direction, and means responsive to an excessive condenservoltage of said predetermined polarity, due to the failure of the charge-reducing means to operate, to return said condenser to said state of charge, to thereby change said output frequency in a direction opposite to said predetermined direction.

1 5. A frequency-control system, comprising an oscillator' the output frequency of which is variable in response to variation of a control voltage, a condenser the voltage on which provides said control voltage, means for charging said condenser in a stepwise manner with a predetermined polarity to correspondingly change said output frequency in a predetermined direction during each of said steps, means for passing at least a portion of the output of said oscillator through a tuned means having a symmetrical frequency-output response characteristic, means responsive to the output of said tuned means for deriving simultaneously with the said output frequency changes pulses of a polarity which reverses when said output frequency reaches the resonant frequency of said tuned means, and means actuated by a pulse of said reverse polarity for reducing the charge of said predetermined polarity on said condenser, to thereby change said output frequency in a direction opposite to said predetermined direction.

16. A frequency-control system, comprising an oscillator the output frequency of which is variable in response to variation of a control voltage, a condenser the voltage on which provides said control voltage, means for charging said condenser in a stepwise manner with a predetermined polarity to correspondingly change said output frequency in a predetermined direction during each of said steps, means for passing at least a portion of the output of said oscillator through a tuned means having a symmetrical frequency-output response characteristic, means for differentiating the output of said tuned means to produce simultaneously with the said output frequency changes pulses of a polarity which reverses when said output frequency reaches the resonant frequency of said tuned means, and means actuated by a pulse of said reverse polarity for reducing the charge of said predetermined polarity on said condenser, to thereby change said output frequency in a direction opposite to said predetermined direction.

MILTON D. RUBIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,211,852 Geiger Aug. 20, 1940 2,250,284 Wendt July 22, 1941 2,434,293 Stearns Jan. 13, 1948 2,445,933 Beste July 27, 1948 2,447,082 Miller Aug. 17, 1948 2,450,360 Schoenfeld Sept. 28, 1948 

